diff --git a/docs/setup.en.md b/docs/setup.en.md
index 29b298c664..25cad92042 100644
--- a/docs/setup.en.md
+++ b/docs/setup.en.md
@@ -54,6 +54,11 @@ As root:
 *6.* Build Misskey
 ----------------------------------------------------------------
 
+Before build, you need to set `NODE_ENV` to `production`. like this:
+* Linux: `export NODE_ENV=production`
+* Windows (PowerShell): `$env:NODE_ENV="production"`
+* Windows (CMD): `set NODE_ENV=production`
+
 Build misskey with the following:
 
 `npm run build`
diff --git a/docs/setup.ja.md b/docs/setup.ja.md
index 2501b86fb0..46e608aa98 100644
--- a/docs/setup.ja.md
+++ b/docs/setup.ja.md
@@ -60,6 +60,11 @@ adduser --disabled-password --disabled-login misskey
 *6.* Misskeyのビルド
 ----------------------------------------------------------------
 
+ビルドする前に、`NODE_ENV`を`production`にする必要があります。例:
+* Linux: `export NODE_ENV=production`
+* Windows (PowerShell): `$env:NODE_ENV="production"`
+* Windows (CMD): `set NODE_ENV=production`
+
 次のコマンドでMisskeyをビルドしてください:
 
 `npm run build`